Development work on electric vehicles and the infrastructure thereof has been underway for a long time. In this context, there is a need to standardize a charging cable, i.e., a charging connection, between the electric vehicle and a charging station for charging a battery of the electric vehicle. FIG. 1 shows an example of the vehicle to be charged as station S2, the charging column as station Sl and the charging connection. In connection with this standardization, the ISO/IEC (ISO=International Standardisation Organisation, IEC=International Electrotechnical Commission) is currently compiling a document IEC 61851-1 Annex A.
FIG. 2 shows an example of a plug PLG of the charging connection VL, which is introduced into a matching counterpart on the electric vehicle. The individual conductors for the plug are physically separate partial connections, each embodied, for example, as a copper cable with an insulating sheath. Here, the individual contacts designate the following functions:    LI, L2, L3: Three outer conductors    N: Neutral conductor    PE: Ground conductor, potential to ground    SC: Control conductor    SP: Signaling conductor
The combination of the conductors LI, L2, L3, PE and N forms a plug which is used for industrial purposes to connect three-phase machines and is defined as Standard IEC 60309. The contact SC (Control Pilot) only indicates whether the plug PLG of the charging connection VL has been inserted in the socket on the vehicle and hence there is a physical connection between the station 1 and the station 2. The signal conductor SP (proximity) is used for the exchange of basic information. Document IEC 61851-1 Annex A suggests the provision of pulse-width modulation (PWM) with which “low level” signaling can be performed on the signal conductor SP. Consideration is also being given to a broadband communication connection via one of the outer conductors LI, L2, L3 with the aid of PLC technology (PLC=Power Line Communication).
Hitherto, it was assumed that signal level analysis can be used to establish whether a charging connection exists, i.e. the charging cable is connected to the vehicle. However, with the increasingly broad bandwidths of PLC connections, this is very unreliable and, at the high currents typically required for the charging process, may require large and expensive components, such as, for example inductors.